The present invention relates to a telephone apparatus suitable for use as a subscriber station and/or an attendant console. More particularly, the invention relates to a digital telephone apparatus which is adapted for connection with a telephone transmission line for full duplex communication between the apparatus and all other units which are connected with the telephone system, such as other subscriber stations, attendant consoles and data recording, storage and processing equipment.
A preferred embodiment of the present invention concerns telephone keyset apparatus; that is, a telephone apparatus having a number of dial, line and function keys. This apparatus may contain one or more of a number of telephone "features" and "functions" as will be described below.
As is well known, the standard telephone apparatus comprises an acoustic/electrical transducer or microphone, an electrical/acoustic transducer or earphone, a hook switch, a dialing mechanism and a bell or buzzer. The structure required to include these features need be no larger than a telephone handset. In fact, telephone instruments are known in which the handset itself has a hook switch which is actuated when the handset is in the rest or "on-hook" position, and deactivated when the handset is lifted off a flat surface into the "off-hook" position for use in communicating.
As the cost of electronic equipment is currently falling, many hardware "features" have been and are being added to this otherwise remarkable invention. Some typical features which a telephone instrument may include are:
(1) a plurality of "line" keys which, when depressed, connect the telephone to different lines; PA1 (2) a plurality of "function" keys which, when depressed, initiate one or more of a number of telephone functions; PA1 (3) a display which images a number of alphanumeric characters; PA1 (4) a microphone for "hands free" speaking; PA1 (5) a speaker for "hands free" listening; PA1 (6) an external unit jack for connecting the telephone to a recording printer, a digital data interface unit, a magnetic recorder for taking messages, a console containing additional line and function keys and/or another peripheral unit such as an external computer, CRT display and the like; and PA1 (7) a small computer which may be utilized by the customer as a programmable element as well as to control the instrument.
Experience has shown that more and more "functions" or modes of operation have been, and will be added to the telephone instrument to make it a most convenient and versatile piece of equipment. Not only will the telephone in the future serve each user as an instrument of voice and data communications, it will also serve other telecommunication functions such as providing music, external paging, message recording and/or dictation access; room and building security against unauthorized access and/or fire; and room and building energy control such as lighting, heat and air conditioning. As mentioned above, the telephone instrument may also serve as a small, handy computer which can operate off-line or in direct communication with another computer at another location.
When designing telephone keyset apparatus--that is, a telephone instrument with a number of keys for dialing and for other functional purposes--it is desirable to take into consideration and to provide for the possibility of implementing the various features and functions such as those enumerated above. More particularly, it is desirable to develop an economical and efficient telephone instrument which is not significantly larger than presently existing telephones and which may be implemented inexpensively as a "modular" device that can readily be tailored to meet the needs of each user. Such a modular structure would facilitate the creation of a "family" of telephones, telephone consoles and other ancillary equipment, from option-laden instruments having all the available features and functions to a basic telephone instrument constructed at minimum cost.
One of the important requisites for a telephone apparatus of the type described above is the ability to connect to a standard, four-wire telephone transmission line and to operate with full duplex communication. Another important requisite is that the apparatus transmit and receive information in digital, not analog, form. Digital telephone systems known in the art utilize two different types of solutions to provide duplex communication with sufficient transmission quality. The first technique requires a plurality of transmission lines: that is, separate lines for PCM voice data in each direction, for signalling and for synchronizing. At least two of these wires are also used to provide DC power to the telephone apparatus. The second technique provides a so-called "ping-pong" type of duplex data transmission. With this technique, the transmission of data in opposite directions is alternately generated in the subscriber station/attendant console, on one hand, and in the telephone system or exchange, on the other. This data is transmitted in separate time periods via a two or four-wire transmission line.
Thus, whereas the first technique provides full duplex transmission by utilizing a multiplicity of wires, the second technique uses only a two or four-wire transmission line but sends data alternately back and forth between the telephone exchange and the subscriber station or attendant console.